7/2016
SATEL technical bulletin
SATELLAR
Dynamic Routing
“A router with dynamically congured routing tables is known as a dynamic router. Dynamic
routing consists of routing tables that are built and maintained automatically through an ongoing
communication between routers. This communication is facilitated by a routing protocol, a series of
periodic or on-demand messages containing routing information that is exchanged between routers.
Except for their initial conguration, dynamic routers require little ongoing maintenance, and therefore
can scale to larger internetworks.
Dynamic routing is fault tolerant. Dynamic routes learned from other routers have a nite lifetime.
If a router or link goes down, the routers sense the change in the internetwork topology through the
expiration of the lifetime of the learned route in the routing table. This change can then be propagated to
other routers so that all the routers on the internetwork become aware of the new internetwork topology.
[https://technet.microso.com/en-us/library/cc957844.aspx]”
Dynamic routing benets:
• Easy setup of routing
• Fast setup of routing
• Load sharing by routing
• Redundancy by routing
SATELLAR support dynamic routing protocol by providing OSPF (Open Shortest Path First) functionality.
SATELLAR uses the OSPFv2 daemon from the Quagga Routing Suite to implement OSPF. More
information, such as full documentation, can be found on the following web page:
http://www.nongnu.org/quagga/
In the following image, there are two redundant paths from SCADA system to remote network. The
router connected to SATELLARs is an OSPF enabled router, and thus the OSPF enabled SATELLARs and
the gateway router will be able to communicate with the dynamic routing protocol. The two SATELLARs
advertise the route towards the remote network. In other words the gateway router will learn from the
protocol that the remote network can be reach via both of the SATELLARs. As a result, it will use the one
with the lower cost as a route towards the remote network.
If the gateway router stops hearing advertisements from the lower cost SATELLAR, it will regard that route
gone and will remove it from its routing tables. Hence, the traic will switch to surviving SATELLAR.
SATEL technical bulletin
SATELLAR
2
SATELLARs may have equal costs to their routing paths. In this case the router R may also carry out load
sharing scheme, if the router R has Equal Cost Multi Path (ECMP) feature enabled. This would make some of
the traic to be forwarded to other path and some proportion of the traic via another path.
Furthermore, the dynamic routing protocol will be able to utilize information from the redundant
routing functionality: if a route monitoring is resulting one or more routes unavailable, the SATELLAR
will remove those routes from its routing table. This will result SATELLAR updating the changed routing
information to the OSPF protocol, and thus the gateway router will know to recalculate its own routing
tables. Consequently, the traic will dynamically be move to a path via the SATELLAR that still has the
corresponding route accessible and in its routing table.
The OSPF protocol is widely used and common, so it will be easy to combine SATELLAR with any other
OSPF enabled device. Thus, the OSPF could be used to provide redundant or shared networking solution by
combining the SATELLAR network together with wired networking or public cellular network.
